1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit breaker trip units.
2. Background Information
Circuit breakers and circuit breaker trip units are well known in the art. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271.
Resetting of a circuit breaker (e.g., through the operating handle and operating mechanism thereof) is accomplished in a manner well known in the art and is described and shown, for example, in U.S. Pat. No. 5,910,760.
As disclosed in U.S. Pat. No. 6,144,271, a linear plunger of the trip unit is employed to trip open the associated circuit breaker frame whenever the linear plunger is extended from the trip unit. Actuation of primary and secondary frame latches occurs exclusively by way of the extended and resetable trip unit linear plunger, which is, otherwise, normally contained entirely within the trip unit. The secondary frame latch is in disposition to be struck by an abutment surface of the extended linear plunger. In response to a reset operation, the trip unit is also reset whenever the secondary frame latch drives the extended linear plunger in the opposite direction against its plunger spring and into the trip unit.
An interchangeable or removable trip unit is a modular device used with industrial circuit breakers that allows the customer to alter the breaker's electrical properties.
In a trip unit, a device called a trip bar actuates a mechanism to trip the breaker. Another component, called a trip actuator, is an electro-mechanical apparatus that operates various mechanism parts in the trip unit, after being activated by a trip signal. After a trip condition, these two components must be reset in order to operate again. Typically, in known prior art trip units, this is accomplished by separate reset levers working independently.
One of the most frequent problems with molded case electronic trip units is the malfunctioning of the tripping device.
The main problem with the existing trip actuators is the inconsistency of their magnets and therefore, the magnetic field. This will affect whether the trip actuator is suitably sensitive to tripping. Also, since the existing technology uses pre-magnetized magnets, the assembly process is difficult.
There is a need for an improved circuit breaker employing a trip unit.
There is also a need for an improved circuit breaker trip unit.